OSX behind ISA Server? does anyone use it?

At work we have ISA Server 2004 and it seems OSX doesn't like it 1 bit.

I can't use mail clients such as outlook and apple mail
I can't access FTP
Also, most recently... 'uploading' seems to have randomly broken. I use CloudApp and also have a MobileMe account. CloudApp did work, but not now.. i can't even login to the app.

MobileMe works great apart from iDisk, i can't access it from OSX mount and i cant upload to it from a browser.

The only browser that works well for me is Chrome... Safari and Firefox love throwing the firewall username and password dialogue box at me and randomly locking websites.

Does anyone have any experience in this area it's driving me crazy.